Solar collection facilities utilize solar concentrators and/or photovoltaic panels for harnessing solar energy. Solar concentrator assemblies (SCAs) utilizing movable parabolic trough collectors present large reflective surface areas (apertures) for tracking the sun and focusing the captured radiant energy on linear heat collection elements (HCEs) as a first step in a thermomechanical conversion process for generating electrical power. A solar-trough solar power generation facility typically includes many SCAs arranged in rows to capture great amounts of solar radiant energy.
The reflective surfaces of troughs of SCAs are usually hot-formed, thick-glass minors that ideally conform to a given geometry, notably surface curvature. Operating efficiency of the solar plant is largely dependant on the ability of the mirrors to maintain surface curvature accuracy, so that the mirrors sharply focus reflected sunlight on the HCE. This requires very exacting manufacturing processes for mirror production and high rigidity of the mirrors themselves as mounted to their supports. Thus, the glass is typically formed thicker, often resulting in a mirror weight that rivals the weight of the supporting structure.
Traditionally, hot-formed, glass mirrors are used in various solar concentrating applications, such as the Nevada Solar One solar power generating plant in Nevada. The glass mirror material is hot-formed to the mathematical shape (surface geometry) required to reflect and concentrate sunlight on an HCE. Such hot-formed glass is also known as sagged glass. Sagged glass is thick, heavy, costly to manufacture, costly to transport and install at a facility, and prone to breakage.
The thick glass mirrors (or any other reflectors utilized) must retain their mathematical shape in order to efficiently focus concentrated sunlight, which requires the hot-formed mirror glass to have a sufficient thickness to maintain the mirror shape (usually about three to five millimeters). Problems with the hot-formed glass include that the thicker glass reduces the reflective efficiency of the mirror (more absorption and less reflection of sunlight), has fabrication-related surface error limitations (slope error and edge effects), is more costly due to the increased amount of glass material, and is heavier resulting in undesirable shipping and handling issues. Additionally, thick sheet material is difficult to form in the complex shapes needed for solar power applications and may trap water in the interface which corrodes the silvering.
In some cases, thin-glass and thin-film have been bonded directly against a pre-formed substrate or aluminum plate having a desired curvature, or to a sandwich panel made with the required surface geometry. Sandwich panels are usually comprised of two sheet metal surfaces bonded to a cellular core such as a honeycomb configuration. Historical problems with thin-glass and thin-film bonded directly against a pre-formed curved substrate or plate, or in combination with honeycomb and other types of closed-cell panel construction, are high cost and their affinity for water intrusion when exposed to weather. Trapped water attacks the preferably aluminum components and penetrates the mirror coatings, causing the mirror silvering to corrode.